1. Field of the Invention
The present invention relates to an information retrieval system that retrieves necessary information from a database.
2. Description of the Prior Art
Prior art database models include hierarchical and network type databases. The prior art relevant to the invention will now be described in connection with a typical hierarchical database.
FIG. 1 is a view showing the data structure of a typical hierarchical database discussed illustratively in "Bit" (a Japanese publication by Kyoritsu Publishing Co., Ltd.), Vol. 23, No. 9, pp. 1297-1308 (1991). As indicated in FIG. 1, the relations between data constitute a tree structure. At the top of the tree structure is a root node followed downward by child nodes which in turn are followed by their child nodes, and so on.
In FIG. 1, reference characters 1a through 1h are record types. The uppermost record type 1a is the root. FIG. 1 shows eight record types 1a through 1h. A line between any two of the record types 1a through 1h indicates the existence of a parent-child relation therebetween.
The constraints on the tree structure include the following:
(1) Each defined tree structure should have one root record. PA1 (2) There should be only one parent record for a given record type.
The order of the record types 1a through 1h in such a tree structure is associated closely with the physical structure of the database. That is, data are reached by sequentially following the record type order 1a through 1h. When using an information retrieval system based on a tree structure database, the user must describe desired data in a sequence that complies with the physical record type order of the database. Otherwise, it would take an inordinately long time to retrieve any desired data from the system.
As described above, given such prior art information retrieval systems, users are obliged to describe desired data under constraints of the physical relations between the data constituting the database of each system. The task of describing the data to be retrieved in the above manner is a tedious, time-consuming chore.
In a more specific example of information storage and retrieval, printed photographs are traditionally put in order when they are suitably arranged in albums or the like together with user-written descriptions of the date and place associated with each photo. Such orderly arrangement of photos typically involves having to develop and print each roll of film every time it is finished with all its picture frames taken. Subsequent retrieval of a desired picture can be quite a challenge if there are a large number of pictures stored more or less haphazardly. These annoying aspects of information storage and retrieval have often proved to be characteristic of the prior art.
In this connection, storage of image information in the form of electronic still pictures is drawing attention today. Electronic still pictures are made of image information entered through an image input device such as CCD (charge coupled device) for storage onto such recording media as magnetic tapes and magnetic or optical discs. The stored information is later retrieved for reproduction on a CRT screen (e.g., TV screen) or as hard copy. Unlike conventional pictures, the contents of such image information cannot be verified visually. This inconvenience contrasts with the ability of electronic still picture systems to store and retrieve large quantities of image information efficiently.
Conventional database management techniques could be applied to the data retrieval of electronic still pictures. However, general users cannot be expected to build a sophisticated database on their own just for the sake of retrieving desired pictures. What is needed is an information retrieval system that dispenses with traditional database retrieval techniques when the database of the system is accessed directly by the user. The system should be constructed in such a manner that the user may readily retrieve desired data therefrom by feeding simple retrieval data thereto.